Conventionally, first generation wireless communication networks were configured to operate at one specified channel rate. Schedulers were not required in the first generation wireless communication networks because only one channel rate was available. Advances in wireless communication technology has introduced third generation wireless communication networks, such as W-CDMA, CDMA 2000 1xRTT and 1xEV-DO, that provide multiple rates and scheduling policies for dynamically transitioning between the multiple rates.
Typically, the scheduling policies for the third generation wireless communication networks select a high channel rate to quickly clear buffer backlogs. Essentially, this policy attempts to optimize output to a user by always utilizing the fastest available channel rate. This type of scheduling policy may be ideal for inelastic applications, such as VOIP, that provide a constant sending rate. For inelastic applications, the high channel rate may be configured to the constant sending rate, so, the channel rate matches the constant sending rate. However, when elastic applications, such as TCP, provide variable sending rates, a scheduling policy that always assigns the highest channel data rate introduces channel rate inefficiencies. For instance, if a TCP sending rate varies between 2 kbps-5 kbps and the scheduling policy assigns a channel rate of 5 kbps there is waste in power and channel bandwidth when the TCP sending rate is 2 kbps. The difference between the channel rate and the TCP sending rate, 3 kbps, is not effectively utilized until the TCP sending rate increases to 5 kbps. In other words, a scheduling policy that always aims to clear buffer backlog can be sub-optimal for TCP because the TCP sender may not effectively utilize the high channel rate. Additionally, the high channel rate may introduce more data errors than a low channel rate.
Modern CDMA wireless channels support multiple transmission rates, which can be dynamically assigned to users based on traffic demand. However, in practice, assignment of high rate channels comes with the penalty of increased power as well as smaller orthogonal codes, which constrains their assignment to only a subset of active users. This motivates the need to carefully control high rate channel assignments so as to minimize power and achieve fairness among users.